a,b,c,d	[-]	material parameters of various multiaxial fatigue strength estimation methods
C	[MPa]	shear stress on an examined plane
$\delta$	[deg]	phase shift of the given stress signal compared with the axial stress signal
$\Delta FI$	[%]	fatigue index error
$FI$	[-]	fatigue index
$\sqrt{J_2}$	[-]	second invariant of the stress tensor deviator
$\kappa$	[-]	ratio of fatigue strengths in fully reversed loadings ($s_{-1}/t_{-1}$)
N	[MPa]	normal stress on an examined plane
$r_{\sigma }$	[-]	stress ratio (${\sigma }_x/{\tau }_{xt}$)
s	[MPa]	fatigue strength in axial loading
$\sigma$	[MPa]	nominal axial stress induced by axial load
${\sigma }_H$	[MPa]	hydrostatic stress
t	[MPa]	fatigue strength in torsion
$\tau$	[MPa]	nominal shear stress induced by torsion
$\theta$, $\phi$	[deg]	Euler angles defining the orientation of the examined plane